The message “client_global_hostkeys_private_confirm: server gave bad signature for RSA key 0” is not an error, it is a warning, and it is related to some ssh versioning issue. It used to be very common to receive from GitLab.
If you want it to go away, you can make sure that your ~/.ssh/config contains the following:
Host gitlab.com
UpdateHostKeys no
However, if you are in fact being prevented from pulling, then this bad signature warning is probably not the reason. Once you make the warning go away, you will still have to find the real problem that you have, about which we know nothing, as the question stands right now.